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Multiple gastric aspirates needed to diagnose children with suspected TB
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BOSTON — Children with suspected tuberculosis infection may require numerous specimens to confirm tuberculosis diagnosis because they can have intermittently positive gastric aspirate cultures, according to findings presented during the 2012 Pediatric Academic Societies Annual Meeting.
Many children with suspected TB are admitted to the hospital when there is no identifiable person with suspected TB in whom cultures and drug susceptibilities could be obtained. Therefore, researchers from Baylor College of Medicine, Houston, launched a study to determine the number of aspirates need to accurately diagnose TB.
“We wanted to figure out how many gastric aspirates you truly needed to subject children to while they were inpatients,” Andrea T. Cruz, MD, MPH, assistant professor, pediatrics, Baylor College of Medicine, Houston, and lead author of the study, said. “It’s a costly procedure, it’s not a comfortable procedure for the children, and there was good data from adult population that indicated two specimens were sufficient and there was little incremental value to getting the third specimen.”
The retrospective case series evaluated children ages younger than 18 years admitted to a tertiary care children’s hospital in Houston between 1998 and 2010. Patients were identified from the microbiology laboratory and TB clinic databases.
Gastric aspirates for acid-fast bacilli (AFB) stain and culture were obtained from all the children using a standardized protocol for collection by nurses. Frequencies were calculated for demographic variables and culture results.
Cruz and colleagues included in their study 280 children (mean age 3 years; 121 female) who had gastric aspirates sent for AFB culture. Thirty-two (11%) children grew Mycobacterium tuberculosis; this represented 39% of this cohort who ultimately were treated for TB disease.
Fifty-three children had one gastric aspirate (none were TB culture positive or treated for TB). A total of 62 children had two gastric aspirates and eight children had at least one positive TB culture. There were 160 children who had three gastric aspirates; 23 grew TB in at least one sample. Five children had four gastric aspirates and one grew TB. Of the four children with a positive AFB smear, three grew TB, and one grew M. kansasii. Only 9% of all children with positive TB cultures were smear-positive.
”The majority of children had at least three cultures sent and we found that with all the children in the population, only about 10% of them were culture positive,” Cruz said. “But among the children who were actually treated for TB, 40% of them were culture positive, and this really fits into more with well established data.”
Of children whose gastric aspirates grew TB, 24 of 32 (75%) grew on first specimen obtained. Second and third gastric aspirates increased diagnostic yield in six (19%) and two (6%) cases, respectively, when prior gastric aspirates were negative.
“We were hoping the results would show that it never grew the third time so we could just do two gastric aspirates, but that wasn’t the case,” she said. “We are left in an ambivalent state because 6% of the time, the first one didn’t grow and the second one didn’t grow but the third one did grow TB.”
Cruz added that at this time, three gastric aspirates remain the standard of care.
For more information:
- Cruz AT. #2913.165. Presented at: 2012 PAS Annual Meeting; April 28-May 1, 2012; Boston.
Perspective
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Richard F. Jacobs, MD
Cruz, Revell and Starke are to be congratulated on such a rigorous and well controlled protocol for obtaining gastric aspirates for evaluation. As outlined, not having a source case/contact for microbiological confirmation and the availability of susceptibility testing challenges both the diagnostic and therapeutic plans for children with TB. The study shows the limitation of acid-fast stained gastric aspirate specimens, which has been well documented for decades. Although the overall culture-positive rates are low, those children are afforded the opportunity to be treated with the best regimen in an era of drug resistance.
This study continues to demonstrate our limitations in diagnosing and confirming drug resistant TB in children or to have the data needed to provide optimal treatment for most children with TB. The authors’ idea of sputum sampling with induction techniques warrants further study. I would hope that newer molecular testing for identification and available drug resistance markers would be added to the protocol.
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